Brunck, Marion Emilie GenevieveCruz Cárdenas, José Antonio2026-02-062025-09-01https://hdl.handle.net/11285/704343https://orcid.org/0000-0001-8994-8276Neutrophils rely on Fc gamma receptors (FcgRs) to recognize IgG-opsonized pathogens, initiating antimicrobial functions such as phagocytosis, reactive oxygen species (ROS) production, cytokine release, and SYK-dependent signaling. CD16b (FcgRIIIb), the most abundant FcgR on human neutrophils, is a GPI-anchored receptor lacking an intracellular domain, and its signaling mechanisms remain poorly understood. The rarity of CD16b deficient neutrophils in the population (<1%) limits direct investigation in primary cells. To address this, we generated HL-60–derived neutrophil-like cell lines with CRISPR/Cas9 mediated deletion of either CD16b or CD32a (FcgRIIa) and performed functional assays including phagocytosis, ROS production, SYK phosphorylation, and cytokine profiling. Both CD16b-/- and CD32a-/- HL-60-derived clones differentiated normally into neutrophil-like cells and retained phagocytic capacity. However, FcgR-mediated ROS production and SYK activation were significantly impaired, particularly in CD16b-deficient cells. Cytokine responses were altered in a receptor-specific manner: CD16b-/- cells produced less IL-6 and IL-1β, whereas CD32a-/- cells produced less TNF-α and IL-10. These results highlight the distinct contributions of CD16b and CD32a to neutrophil effector functions and immune regulation. Complementing the model, we identified two healthy brothers naturally lacking CD16b on their neutrophils. Sequencing revealed mutations in exon 2 of FCGR3B resulting in loss of protein expression. FcgRIIIbnull neutrophils exhibited compensatory upregulation of CD16a and CD64 but showed impaired phagocytosis, ROS production, actin polymerization, and SYK-dependent signaling following stimulation with opsonized E. coli. Altered surface expression of FcgRIa, TLR-4, and CD11b was also observed upon bacterial challenge, suggesting broader regulatory effects of CD16b on neutrophil activation. Overall, this study combines engineered cellular models and rare human phenotypes to demonstrate that CD16b is a critical regulator of neutrophil antimicrobial functions and signaling. These findings provide mechanistic insight into FcgR biology and establish platforms for future investigation of receptor-specific contributions to neutrophil functions.TextoengopenAccesshttp://creativecommons.org/licenses/by/4.0MEDICINA Y CIENCIAS DE LA SALUD::CIENCIAS MÉDICAS::PATOLOGÍA::INMUNOPATOLOGÍABIOLOGÍA Y QUÍMICA::CIENCIAS DE LA VIDA::INMUNOLOGÍA::INMUNOLOGÍAScienceTesis de doctoradoPor política las tesis de Ciencias Exactas y Ciencias de la Salud estarán en embargo por 1 añoNeutrophilsFc gamma receptorsCD16b1007842